1. Field of the Invention
The present invention relates to a fluorescent lamp which includes a conventional bulb containing therein a coating of phosphor powder. The phosphor powder used has been ground to provide a substantial decrease in fluorescent lamp phosphor powder weight without any loss in light output.
2. Description of the Prior Art
Fluorescent lamps have various shapes and forms. One typical fluorescent lamp is in the form of an elongated soda-lime silicate glass bulb having a circular cross section. The lamp includes a conventional discharge assembly including an electrode structure at each end of the bulb supported therein by lead-in wires which are sealed in and extend through a glass seal in a stem mount to the contacts of a lamp base affixed to opposite ends of the lamp. The sealed glass tube contains a conventional discharge sustaining filling. The inner surface of the elongated glass bulb is coated with phosphor, the phosphor coating typically covering the entire length of the inner wall of the bulb. The lamp is coated in a conventional manner. One of the factors considered during the phosphor coating operation is that the coating be effected to the extent required to obtain the desired degree of light output. The coating process is an important factor in defining the lamp optical density and lumen output. In evaluating these factors it has been observed that the average particle size of the phosphor powder is an important consideration in obtaining the desired results. Ordinarily there will be a distribution of bright, coarser phosphor particles in the 17 to 35 micron range, intermediate sized bright phosphor particles in the 6 to 13 micron range and lower brightness particles in the 3 to 6 micron range. In using conventional phosphor powder a given powder weight will be required depending upon the specific make-up of the phosphor powder and the desired results. One problem encountered in coating a bulb with conventional phosphor powder is that the presence of the coarser particles provides a smaller powder surface area within the bulb thereby providing less than optimum lamp coating coverage. To obtain the desired optical density, a higher than desired total phosphor weight is required. This adds to the cost of the lamp.
It is an object of the present invention to provide a method of coating a fluorescent lamp with phosphor powder which has been ground to the extent that there is a substantial decrease in phosphor powder weight without any loss in light output. It is a further object of the present invention to provide such a method wherein the reduction in phosphor powder weight provides a substantial savings in phosphor cost. It is another object of the present invention to provide a method which allows for a decrease in phosphor powder weight at the same lamp density and lumen output as was obtained heretofore with the use of conventional unground phosphor. Yet another object of the present invention is to provide a fluorescent lamp which embodies the foregoing characteristics.